The present invention relates to a semiconductor device, for example, a semiconductor device incorporated into an inverter system.
An inverter control used for a motor control has been known. The inverter control is used for home appliances such as an air conditioner, a refrigerator, or a washing machine, or industrial machines. For example, Japanese Unexamined Patent Application Publication No. 2009-95206 (corresponding U.S. Pat. No. 8,139,385B2) discloses an inverter control circuit that conducts the inverter control. The inverter control circuit is configured to control the inverter circuit including a switch element. The inverter control circuit includes a timer circuit, an amplifier, and a gain control circuit. The timer circuit generates a PWM signal for controlling a conduction state of the switch element. The amplifier receives, amplifies, and outputs an analog signal generated by a load current of the inverter circuit. The gain control circuit controls switching of a gain of the amplifier in synchronization with an output change timing of the PWM signal.
As a related art, Japanese Unexamined Patent Application Publication No. 2004-210233 (corresponding U.S. Pat. No. 7,366,599B2) discloses an electric power steering device. The electric power steering device is configured to transmit a driving force of an electric motor to a steering mechanism to assist steering. The electric power steering device includes a current detector circuit, a microcomputer, and a gain changing unit. The current detector circuit is configured to detect a current flowing in the electric motor, and output a motor current detection signal. The current detector circuit outputs a motor current detection signal amplified by a variable gain amplifier circuit that can change the gain. The microcomputer has an analog/digital conversion port that receives the motor current detection signal output by the current detector circuit, and controls the electric motor on the basis of the motor current detection signal captured through the analog/digital conversion port. The gain changing unit changes the gain of the variable gain amplifier circuit. The variable gain amplifier circuit is configured such that a current flows into an analog switch SW. For that reason, an influence of an on-resistance of the analog switch SW causes an error to be generated in the gain of a differential amplifier.
Also, Japanese Unexamined Patent Application Publication No. 2001-298337 discloses a gain variable amplifier circuit. The gain variable amplifier circuit includes an operational amplifier, a gain switching resistor group, a plurality of analog switches, and a selector unit. The gain switching resistor group has a plurality of resistors connected in series with each other. The plurality of analog switches is connected between halfway points of the respective resistors in the gain switching resistor group, and an input terminal of the operational amplifier. The selector unit selectively turns on any one of all the analog switches. The gain variable amplifier circuit is configured such that no current flows into the analog switches. For that reason, the influence of the on-resistance of the analog switch SW does not cause an error to be generated in the gain of the operational amplifier, and the signal can be amplified with high precision. In this case, a common mode rejection ratio (CMRR) of the operational amplifier is degraded, and the common mode rejection ratio (CMRR) is changed by a change in the gain.
Also, Japanese Unexamined Patent Application Publication No. 2011-254561 (corresponding European Patent Publication No. EP2388599A2) discloses a motor current detection IC. The motor current detection IC includes a differential amplifier circuit, a pair of input terminals or a non-inverting input terminal and an inverting input terminal of the differential amplifier circuit, and an output terminal of the differential amplifier circuit. The input terminals of the differential amplifier circuit can receive a negative voltage. The input terminals of the differential amplifier circuit have a function of blocking a terminal to which an excessive voltage is input at the time of inputting the excessive voltage.